Search for supernova produced 60Fe in Earth's microfossil record

Search for supernova produced 60Fe in Earth's microfossil record

Ludwig, P.; Bishop, S.; Egli, R.; Faestermann, T.; Famulok, N.; Fimiani, L.; Gómez Guzmán, J. M.; Hain, K.; Korschinek, G.; Hanzlik, M.; Merchel, S.; Rugel, G.

Nucleosynthesis in massive stars can produce copious amounts of the radioisotope 60Fe (T(1/2)= 2.62 Ma). When those stars end their lives in a supernova, material enriched with nucleosynthesis products can be ejected into the interstellar medium. If such supernova debris is picked up by Earth, it can be incorporated into terrestrial reservoirs. After the discovery of live 60Fe atoms in 2-3 Myr old layers of a Pacific Ocean ferromanganese crust (K. Knie et al., Phys. Rev. Lett., 93(2004) 171103), a confirmation of this signal, as well as a mapping of the signal with high time-resolution is desirable. Another reservoir in which the 60Fe signature should have been incorporated in are the fossils of magnetotactic bacteria in ocean sediment. These bacteria form chains of small magnetite crystals for magnetotaxis. After cell death and sedimentation, these magnetic chains can be preserved even over geologically significant timescales. In order to extract iron from secondary, 60Fe bearing minerals only, a carefully tuned chemical leaching technique was employed. A novel technique to characterize this procedure using magnetic measurements was also developed applied to quantify secondary magnetite in our samples. As sample materials, two sediment cores from the Eastern Equatorial Pacific were obtained and processed. The concentration 60Fe/Fe was then measured with accelerator mass spectrometry at the GAMS setup in Garching. It features a gas-filled magnet, allowing for complete isobar suppression in the case of 60Fe and 60Ni, leading to a sensitivity which can reach even below 60Fe/Fe = 1E-16. Additionally, one of the sediment cores was also analyzed for 10Be and 26Al for independent dating of the samples at the DREAMS facility in Dresden.

Keywords: accelerator mass spectrometry; supernova; cosmogenic radionuclide

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Publ.-Id: 20150